Substituent Effects in Pentacenes
A R T I C L E S
Hz), 1.7 (s, 24H). 13C NMR (125.68 MHz, CDCl3): δ 137.6,
137.5, 135.6, 129.0, 128.5, 127.5, 127.2, 126.8, 125.0, 123.7,
20.0. MS-LDI m/z: 694 [M+]. UV-vis λmax (nm): 618, 569,
529. HRMS (FAB) m/z ) 694.3575, calcd m/z ) 694.3599
(Error ) -3.6 ppm).
128.5, 128.0, 127.9, 127.8, 125.6, 72.6, 70.7. LDI-MS m/z: 944
[M+], 927 [M+ - OH], 911 [M+ - 2(OH)]. To a solution of
crude 2,3,9,10-tetrakis-[(phenylmethoxy)methyl]-6,13-diphenyl-
6,13-dihydropentacene-6,13-diol (0.24 g, 0.25 mmol) in acetone
(10 mL) was added dropwise a solution of SnCl2 (0.34 g, 1.79
mmol) in 50% glacial acetic acid (5 mL). The mixture was
stirred at RT for 2 h. The blue precipitate was filtered, and the
solids were washed with water and dried to afford pure 2,3,9,10-
tetra[(phenylmethoxy)methyl)]-6,13-diphenylpentacene, 8, in
2,3,9,10-Tetra[(phenylmethoxy)methyl)]-6,13-diphenylpenta-
cene (8). To a dry 500 mL three-neck flask equipped with a
thermometer and a dropping funnel was added a solution of
dry CH2Cl2 (75 mL) and oxalyl chloride (3.35 mL, 35.23 mmol)
under Ar. The stirred solution was cooled to -78 °C, and a
solution of DMSO (5 mL, 0.07 mol) in CH2Cl2 (13 mL) was
added dropwise. This solution was stirred for 5 min before a
solution of 4,5-bis[(phenylmethoxy)methyl]benzene-1,2-dimeth-
anol35 (4.55 g, 12.03 mmol) in CH2Cl2/DMSO (25 mL) was
added dropwise. The reaction was allowed to continue for 0.5 h,
and then triethylamine (40 mL, 0.28 mol) was slowly added at
-78 °C. The reaction mixture was stirred for 10 min and then
allowed to warm slowly to RT. Ice-cold water (50 mL) was
added to the reaction mixture, and the aqueous layer was
extracted with CH2Cl2 (2 × 50 mL) and then dried over CaCl2.
Evaporation of solvent gave crude 4,5-bis[(phenylmethoxy)m-
ethyl]benzene-1,2-dicarbaldehyde which was further purified by
silica gel column chromatography using hexane/ethyl acetate
(70:30) as eluant to yield pure 4,5-bis[(phenylmethoxy)meth-
yl]benzene-1,2-dicarbaldehyde in 70% yield (3.15 g). 1H NMR
(500 MHz, CDCl3): δ 10.54 (s, 2H), 8.08 (s, 2H), 7.35 (m, 10H),
4.65 (s, 4H), 4.59 (s, 4H). 13C NMR (125.68 MHz, CDCl3): δ
192.3, 142.6, 137.5, 135.6, 130.9, 128.7, 128.1, 128.0, 73.2,
68.7. 4,5-Bis[(phenylmethoxy)methyl]benzene-1,2-dicarbalde-
hyde (1.35 g, 3.61 mmol) and 1,4-cyclohexanedione (0.21 g,
1.88 mmol) were stirred in 60 mL of ethanol. To this was added
10 mL of 5% KOH dropwise with stirring. Upon addition of
the first drop, the solution darkened, and solids began to
precipitate. The reaction mixture was stirred at RT for 1 h and
then boiled for 2 h. After cooling to RT, the solids were filtered,
washed with water, and then dried to give yellow-brown
2,3,9,10-tetrakis-[(phenylmethoxy)methyl]pentacene-6,13-di-
1
82% yield (0.19 g). H NMR (500 MHz, CDCl3): δ 8.29 (s,
4H), 7.76 (s, 4H), 7.72 (m, 4H), 7.68 (m, 2H), 7.63 (m, 4H),
7.34 (m, 16H), 7.30 (s, 4H) 4.71 (s, 8H), 4.56 (s, 8H). 13C NMR
(125.68 MHz, CDCl3): δ 139.7, 138.3, 137.2, 134.0, 131.9,
130.5, 129.0, 128.8, 128.6, 128.5, 128.0, 127.9, 127.8, 125.6,
72.6, 70.7. LDI-MS m/z: 911 [M+], UV-vis λmax (nm): 600,
554, 515. HRMS (FAB) m/z ) 910.4010, calcd m/z ) 910.4022
(Error ) -1.3 ppm).
6,13-Diphenylpentacene (9). 6,13-Diphenyl-6,13-dihydropen-
tacene-6,13-diol was prepared as previously described36 in 72%
1
yield. H NMR (500 MHz, CDCl3): δ 8.44 (s, 4H), 7.96 (m,
4H), 7.56 (m, 4H), 6.88 (t, 2H, J ) 7.20 Hz), 6.79 (m, 8H).
13C NMR (125.68 MHz, CDCl3): δ 142.6, 139.6, 132.8, 128.3,
127.8, 127.5, 127.1, 126.5, 125.4, 76.5. LDI-MS m/z: 464 [M+],
447 [M+-OH], 430 [M+-2(OH)]. A suspension of 6,13-diphenyl-
6,13-dihydropentacene-6,13-diol (0.5 g, 1.08 mmol), NaI (1.10
g, 7.34 mmol) and sodium hypophosphite monohydrate (1.21
g, 11.42 mmol) in glacial acetic acid (25 mL) was boiled for
1.5 h under N2 in a round-bottom flask that was equipped with
a reflux condenser. The flask was wrapped in foil to block
ambient light. After cooling, the reaction mixture was filtered
and washed with water (50 mL) and methanol (25 mL). After
drying at reduced pressure, compound 9 was obtained in 88%
yield (0.41 g). 1H NMR (500 MHz, C6D6): δ 8.60 (s, 4H), 7.58
(m, 4H), 7.45 (m, 4H), 7.40 (m, 2H), 7.36 (m, 4H), 6.89 (m,
4H). 13C NMR (125.68 MHz, CDCl3): δ 139.8, 137.1, 131.9,
131.1, 128.8, 128.7, 128.7, 127.9, 125.7, 125.3. LDI-MS m/z:
430 [M+], UV-vis λmax (nm): 604, 558, 519. HRMS (FAB)
m/z ) 430.1703, calcd m/z ) 430.1722 (Error ) -4.4 ppm).
1
one (0.68 g, 46%). H NMR (500 MHz, CDCl3): δ 8.92 (s,
4H), 8.17 (s, 4H), 7.39 (m, 16H), 7.35 (m, 4H), 4.80 (s, 8H),
4.64 (s, 8H). 13C NMR (125.68 MHz, CDCl3): δ 183.1, 138.6,
138.0, 134.9, 131.0, 129.6, 129.5, 128.7, 128.1, 128.1, 73.0,
69.9. LDI-MS m/z: 789 [M+]. A solution of 2,3,9,10-tetrakis-
[(phenylmethoxy)methyl]pentacene-6,13-dione (0.2 g, 0.25 mmol)
was stirred under N2 and cooled to -78 °C in a dry ice/acetone
bath. Upon cooling, phenyllithium (1.8 M, 5.41 mL, 9.74 mmol)
was added dropwise over 10 min. The resulting dark green
solution was allowed to warm to RT and then stirred for 14 h.
The reaction mixture was quenched with 1 M HCl (50 mL)
and the resulting orange brown solution was extracted with
CH2Cl2 (100 mL), washed with water, and then dried over
CaCl2. The solvent was evaporated until only ∼10 mL remained,
at which point hexanes (100 mL) were added, resulting in the
formation of a brown precipitate, crude 2,3,9,10-tetrakis-
[(phenylmethoxy)methyl]-6,13-diphenyl-6,13-dihydropentacene-
6,13-diol. The diol was isolated by vacuum filtration (0.23 g,
95%). The crude diol was not subjected to further purification.
1H NMR (500 MHz, CDCl3): δ 8.29 (s, 4H), 7.76 (s, 4H), 7.72
(m, 4H), 7.68 (m, 2H), 7.63 (m, 4H), 7.34 (m, 16H), 7.30 (s,
4H) 4.71 (s, 8H), 4.56 (s, 8H). 13C NMR (125.68 MHz, CDCl3):
δ 139.7, 138.3, 137.2, 134.0, 131.9, 130.5, 129.0, 128.8, 128.6,
2,3,9,10-Tetramethyl-6,13-diphenylpentacene (10). Initially,
4,5-dimethylbenzene-1,2-dicarbaldehyde was prepared as de-
scribed by Farooq.33 4,5-Dimethylbenzene-1,2-dicarbaldehyde
(1.0 g, 6.17 mmol) and 1,4-cyclohexanedione (0.38 g, 3.39
mmol) were stirred in 60 mL of ethanol. To this was added 10
mL of 5% KOH dropwise with stirring. Upon addition of the
first drop, the solution darkened, and solids began to precipitate.
The reaction mixture was stirred at RT for 1 h and then boiled
for 2 h. After cooling to RT, the solids were filtered, washed
with water, and dried to give crude, brown 2,3,9,10-tetrameth-
ylpentacene-6,13-dione (1.00 g, 81%). LDI-MS m/z: 364 [M+].
2,3,9,10-Tetramethylpentacene-6,13-dione (0.5 g, 1.37 mmol)
was reacted with a solution of phenyllithium (1.8 M, 4.57 mL,
8.23 mmol) as described above to give crude 2,3,9,10-tetram-
ethyl-6,13-diphenyl-6,13-dihydropentacene-6,13-diol (0.54 g,
75%, LDI-MS m/z: 520 [M+], 503 [M+ - OH], 486 [M+
-
2(OH)]). The diol (0.5 g, 0.96 mmol) was reacted with NaI (1.00
g, 6.67 mmol) and sodium hypophosphite monohydrate (1.10
1
g, 10.38 mmol) to furnish 10 (0.43 g, 91%). H NMR (500
MHz, CDCl3): δ 8.14 (s, 4H), 7.70 (m, 4H), 7.65 (m, 2H), 7.62
(m, 4H), 7.48 (s, 4H), 2.35 (s, 12H). 13C NMR (125.68 MHz,
CDCl3): δ 140.2, 136.3, 135.5, 132.0, 130.7, 128.7, 128.5, 127.6,
(35) Meissner, R.; Garcias, X.; Mecozzi, S.; Rebek, J., Jr. J. Am. Chem.
Soc. 1997, 119, 77–85.
(36) (a) Allen, C. F. H.; Bell, A. J. Am. Chem. Soc. 1942, 64, 1253. (b)
Maulding, D. R.; Roberts, B. G. J. Org. Chem. 1969, 34, 1734.
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